WEDNESDAY, March 4 (HealthDay News) -- Despite some improvements, U.S. school meal programs are still laden with unhealthy fat, salt and sugar, nutrition experts contend.

Students also have limited choices in foods available in vending machines, á la carte in cafeterias, at school stores and snack bars and for fund-raisers, they say in a series of articles in a supplement to the February issue of the Journal of the American Dietetic Association.

Echoing these sentiments, a Chicago chef brought to the White House to cook for the Obamas has said that too much of the food available at schools also is high in additives and preservatives.

Unhealthy eating at school, these food experts believe, is contributing to the surge in obesity rates among U.S. children. Obesity rates have more than doubled among infants and toddlers aged 2 to 5, quadrupled in children aged 6 to 11 and more than tripled among adolescents aged 12 to 19, according to an editorial in the journal.

The rising rates have health experts concerned about a nascent epidemic of obesity-related diseases, including cardiovascular disease and type 2 diabetes, in young people.

"Of course, school meals are only one part of the problem," said Anne R. Gordon, a senior researcher at Mathematica Policy Research in Princeton, N.J., and co-author of a paper on school lunches in the supplement. "Kids don't eat well throughout the day. But, we do find at least some evidence that in some of the schools that restrict the availability of sugar-sweetened beverages, you don't see the kids going and drinking more sugar-sweetened at other times of day. It really does decrease intake, so that's encouraging."

Gordon's paper described and assessed data from the third School Nutrition Dietary Assessment, sponsored by the U.S. Department of Agriculture and conducted by Mathematica, as well as findings from other studies that used the same data. The USDA-backed analysis covered both the National School Lunch Program, which provides subsidized meals to about 30 million children daily, and the School Breakfast Program, which provides meals to about 10 million children a day.

The lunch program began in 1946 to help ensure that U.S. children were receiving enough nutritious food. The breakfast program was institutionalized in 1975. Both offer free or low-cost meals to eligible students.

"It's very clear that USDA needs to update the standards of schools" related to nutrition, Gordon said. "They know what they're aiming for, but … having standards is not enough."